Pimavanserin, a selective 5-HT2A inverse agonist without dopaminergic, adrenergic, histaminergic, or muscarinic effect [141], has been approved by the FDA [142] in September 2014 and has shown to be effective and safe in the treatment of PD psychosis, reducing hallucinations and delusions without affecting motor function [143, 144], which is a commonly observed drawback of most antipsychotic drugs due to dopamine antagonism. The gene discussed is HTR2A; the disease is Parkinson disease.